Capillary gas chromatography is one of the most important methods used for chemical analyses. There will probably always be a desire to improve the sensitivity and selectivity of capillary gas chromatography. Capillary gas chromatography was advanced by the use of a retention gap, i.e., a section of capillary tubing preceding the column that is deactivated but not coated with a stationary phase. It is possible to inject a relatively large volume of a liquid sample on-column directly into the retention gap so that a component of the sample can be chromatographed with increased sensitivity. However, when this is done the sample solvent peak is very large and tends to overlap and obscure peaks that correspond to sample components that otherwise are only slightly more retained than the solvent of the sample even though the slightly more retained peaks then elute at a longer retention time.
Noy et al., Journal of High Resolution Chromatography & Chromatography Communications, February 1988, (181-186), disclosed venting away to waste most of the injected sample solvent (hexane) between a cold trap (incorporating an uncoated section of capillary tubing) and a capillary gas chromatography column. However, when this was done there was a significant reduction of recovery for the sample components of interest more volatile than C20 hydrocarbon (C10-C26 hydrocarbons were tested) and with essentially complete loss of C10 hydrocarbon. There is a need for an on-column injection capillary gas chromatography system using a retention gap for injecting very large volumes of samples containing sample components of interest that are only slightly less volatile than the solvent of the sample.